The present invention relates to new kinds of carbon black that are especially suitable as reinforcing carbon black for the rubber industry and a process for manufacturing these carbon blacks. In a further aspect, the present invention relates to articles of manufacture containing the new types of carbon black.
The most important industrial carbon black manufacturing processes are based on the oxidative pyrolysis of carbon black feedstocks containing carbon. In the known processes the carbon black feedstocks are incompletely burned in the presence of oxygen. This category of carbon black manufacturing processes includes, for example, the furnace black process, the gas carbon black process, and the lamp black process. For the most part polynuclear aromatic carbon black oils are used as the carbon black feedstocks. The product stream in oxidative pyrolysis consists of an off-gas containing hydrogen and carbon monoxide and the dispersed carbon black suspended in it, which is separated from the off-gas in a filter unit. The carbon black that is obtained in this manner is then transformed into small beads or pellets for the most part in a wet or dry pellitizing process to make it easier to handle. The moisture in the carbon black arising from the manufacturing process is reduced through a subsequent drying down to under 1% by weight.
Over 90% of the carbon black that is produced industrially is used as a filler and reinforcer in the manufacture of rubber mixtures for the tire industry. Typical rubber mixtures contain 20 to 70% by weight natural and/or synthetic rubber, 20 to 50% by weight carbon black, mineral oils, and other process materials, as well as sulfur as a vulcanization agent.
The carbon blacks with their specific properties affect the abrasion resistance, the rolling resistance, and the wet traction of the finished tires. For rubber mixtures that are used for tire treads a high abrasion resistance and at the same time the least possible rolling resistance and good wet traction are demanded. Low rolling resistance leads to low fuel consumption for the car.
Rolling resistance and wet traction are affected by the viscoelastic behavior of the tread mixture. When there is periodic deformation, the viscoelastic behavior can be described by the mechanical dissipation factor tan .delta. and in the event of elongation or compression by the dynamic elasticity modulus .vertline.E*.vertline.. Both figures are very temperature-dependent. In this connection, the wet traction is usually correlated with the dissipation factor tan .delta..sub.0 at about 0.degree. C. and the rolling resistance with the dissipation factor tan .delta..sub.60 at about 60.degree. C. The higher the dissipation factor at the low temperature, usually the better is the wet traction of the tire mixture. For reducing rolling resistance, on the other hand, as small as possible a dissipation factor is required at the high temperature.
The abrasion resistance and the viscoelastic characteristics and thus also the dissipation factor of the tread mixtures, are essentially determined by the properties of the reinforcing carbon blacks that are used.
An important determining factor is the specific surface area, in particular the CTAB surface area, which is a measure of the portion of the carbon black surface which is accessible to polymer content. As the CTAB surface increases, the abrasion resistance and tan .delta. rise.
Further important carbon black parameters are the DBP absorption as a figure measuring the initial structure and the 24M4-DBP absorption as a measure of the remaining structure after strong mechanical compression of the carbon black.
Carbon blacks that have CTAB surface area between 80 and 180 m.sup.2 /g and 24M4-DBP absorption values between 80 and 140 ml/100 g are most suitable for tread mixtures.
It has been shown that ordinary carbon blacks cannot influence the temperature dependency of the dissipation factor tan .delta. sufficiently in such a way that the tread mixture has a low rolling resistance with the same or better wet traction. The desired reduction in rolling resistance is generally linked with a deterioration of the wet traction and tread wear. Carbon blacks that have a low rolling resistance are designated as so-called "low hysteresis" carbon blacks.
In recent years it has been shown that the rolling resistance of tires can be reduced through complete or partial substitution of carbon black by silica (DP 0 447 066 A1). In order to link the silica with the polymer components of the rubber, silane coupling agents are required. Rubber mixtures containing silica have a dissipation factor tan .delta. that is reduced up to 50%.
An object of the invention is to make available new kinds of carbon black that give rubber mixtures of natural or synthetic rubber or mixtures thereof reduced rolling resistance and at the same time improved wet traction and increased abrasion resistance.